3 results
Biogeochemical formation of metalliferous laminations in surficial environments
- Part of
- Anicia Henne, Dave Craw, Jessica Hamilton, Anat Paz, Gemma Kerr, David Paterson, Jeremiah Shuster, Gordon Southam
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- Journal:
- Mineralogical Magazine / Volume 85 / Issue 1 / February 2021
- Published online by Cambridge University Press:
- 28 January 2021, pp. 49-67
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- Article
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Finely laminated (cm–μm scale) metalliferous precipitates are widespread in the surficial environment, especially around mineral deposits and reflect biogeochemical processes that can pervade near-surface environments on a larger scale. Examples in this paper involve precipitates of the transition metals Fe, Cu and Mn with minor Co, Ni, V and Zn; the metalloids As and Sb; and authigenic Au. Mobility and re-precipitation are driven primarily by geochemical disequilibrium, especially with respect to pH and redox states, that arises from complex interactions between biological processes, geological processes, and variations in the surrounding environment. Different degrees of chemical disequilibrium arise on small spatial scales on time scales of days to millennia. Interactions between biota, waters and rocks in these small near-surface settings affect the biogeochemical environments. Sulfur- and iron-oxidising bacteria are common biogeochemical agents associated with sulfide-bearing lithologies, but localised reductive environments can also develop, leading to gradients in pH and redox state and differential metal mobility. In general, there is commonly a spatial separation of Fe-rich precipitates from those with Cu and Mn, and other transition metals also follow Cu and Mn rather than Fe. Metalloids As and Sb have a strong affinity for Fe under oxidising conditions, but not under more reducing conditions. However, complex biogeochemical parageneses of laminated metalliferous deposits preclude prediction of finer formation details. The textures, mineral species, and metal associations within these deposits are likely to be encountered in all facets of mineral deposit development: initial exploration activity of near-surface locations, mining of shallow portions of orebodies, especially supergene zones, and downstream environmental management with respect to discharging metalliferous waters.
6 - Applications of Scanning Electron Microscopy in Geomicrobiology
- from Part III - Imaging Techniques
- Edited by Janice P. L. Kenney, MacEwan University, Edmonton, Harish Veeramani, Carleton University, Ottawa, Daniel S. Alessi, University of Alberta
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- Book:
- Analytical Geomicrobiology
- Published online:
- 06 July 2019
- Print publication:
- 18 July 2019, pp 148-165
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- Chapter
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Summary
From mineralized biofilms of ancient or “extreme” environments to the nth replicate of laboratory-based biofilm experiments, geomicrobiological samples containing microbes associated with primary minerals or secondary (biogenic) mineral precipitates are highly diverse. The foremost advantage of scanning electron microscopy for geomicrobiology is that it provides high-resolution micrographs of cells and biofilms in association with minerals. These micrographs provide visual evidence of biogeochemical processes, which helps to explain phenomena that occur in the natural environment or in the laboratory. In addition to high-resolution secondary electron or backscatter electron modes of imaging, scanning electron microscopes can be equipped with a range of microanalytical tools, thereby extending the breadth of analytical capacities. Analytical techniques such as energy dispersive spectroscopy and electron backscatter diffraction analysis characterize the chemical composition and crystallography of biofilms and (bio)minerals, respectively, down to the micrometer scale. In addition, a focused ion beam can be used for nanomachining samples to provide a view beneath the outer surface of a sample or can be used as a technique for preparing samples for transmission electron microscopy. To provide the reader with an overview of tools and techniques, this chapter will explain a number of widely used preparation techniques, including whole-mounts, petrographic thin sections, polished blocks, and focused ion beam milling. By using these techniques, various types of geomicrobiological materials will be examined and used to guide and develop the necessary skills for interpreting biogeochemical processes from structural and chemical information obtained through secondary electron and backscatter electron micrographs and associated microanalyses.
7 - Applications of Transmission Electron Microscopy in Geomicrobiology
- from Part III - Imaging Techniques
- Edited by Janice P. L. Kenney, MacEwan University, Edmonton, Harish Veeramani, Carleton University, Ottawa, Daniel S. Alessi, University of Alberta
-
- Book:
- Analytical Geomicrobiology
- Published online:
- 06 July 2019
- Print publication:
- 18 July 2019, pp 166-186
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- Chapter
- Export citation
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Summary
Geomicrobiological samples obtained from the natural environment or from laboratory-based experiments often contain microbial cells, primary minerals, and/or (biogenic) secondary minerals as extracellular precipitates on cell surfaces. The advantage of transmission electron microscopy is that it provides high-resolution imaging of ultrafine structures of cells and minerals. Transmission electron microscopes can be equipped with a range of microanalytical tools, such as selected area electron diffraction and energy dispersive spectroscopy, that complement the imaging capacities of the electron microscope. These two analytical techniques are used to characterize the crystallography and chemical composition of (secondary) minerals, respectively. In addition, lift-outs that have been focus ion beam milled from rock-like materials are analogous to ultrathin sections and can be characterized in a similar manner using transmission electron microscopy. This chapter will demonstrate conventional techniques for preparing samples as whole-mounts and ultrathin sections, which provide a three-dimensional and two-dimensional perspective of samples, respectively. Whole-mounts and ultrathin sections are the most fundamental sample preparation techniques that can be used to characterize geomicrobiological materials. Therefore, in geomicrobiological studies, transmission electron microscopy is an ideal technique to demonstrate and interpret the structure–function relationship of how microbes contribute to the biogeochemistry of a given system.